wheel wit low friction bearing takes 1.0 h to stop after the motor power is turned off. The flywheel was originally rotating at 5.5 rad/s. How many revolutions does the flywheel make before it stops?

Answer 1

Let w = ang vel = w₀+αt ... So with w₀=5.5 rad/sec and with a period of 1 hour (3600 sec) we get 0=5.5+α3600, thus α=-5.5/3600 rad/sec². Note that Φ=Φ₀+w₀t+1/2αt² where φ is the angle thru which the wheel has rotated. If φ0=0, φ can be then calculated to be 9900 radians. Note that one revolution is 2pi radians thus the number of revolutions is 1576.